Currently, the paper and pulp industry generates approximately 50 million tons of kraft lignin.1 In 2014, 125 million liters of cellulosic ethanol were produced commercially in the United States, meeting the volume mandated by the Renewable Fuel Standard for the first time. In 2016, this production is expected to increase to 780 million liters per year. Significantly, for every liter of cellulosic ethanol produced, approximately 0.5-1.5 kg of lignin will be co-generated depending on the nature of lignocellulose used in the process.
The controlled deconstruction of lignin into aromatic platform chemicals and high-octane fuel additives is essential for ensuring the economic viability of the next generation of cellulosic ethanol bio-refineries.2,3 However, lignin valorization remains a challenge due to its inherent heterogeneity, recalcitrance, diversity of inter-aromatic ring linkages, and complex three-dimensional polymeric structure composed of C—C and C—O bonds.2-4 
In this context, a number of catalytic and thermochemical approaches for lignin depolymerization have been explored. Hydrogenolysis of lignin involving simultaneous depolymerization and hydrogenation have been carried out over heterogeneous metal catalysts with externally added H2.5,6,7 Supported metal catalysts such as Pd/C8; H-BEA-35/Raney Ni9; Ni/C10, Pt/Al2O311; and requiring an external hydrogen donor have been used for lignin deconstruction. In these experiments, at 150-300° C., lignin is reported to yield 50% aromatic monomers. Lignin depolymerization over Ni/C12,13 and Pt/C14 catalysts have been studied, where the catalyst enables in situ production of hydrogen from methanol12,13 or formic acid14 solvent. Catalysts such as methylrhenium trioxide,15 and Pd/γ-Al2O3,16 ionic liquid,17 MgO,18 perovskite-type oxide and CuO/Fe2(SO4)3/NaOH20 have been used to catalyze lignin depolymerization in the presence of H2O2 or O2.
Homogeneous metal complexes and salts of Ru, Mn and CO can depolymerize lignin models and lignin.21-25 Rahimi et al.,26 developed metal-free oxidation strategies for lignin and lignin model compounds.
Recently, alkaline catalysts, such as NaOH, KOH, CsOH etc. have been used in a base-catalyzed depolymerization (BCD) of lignin into aromatic monomers.27-30 The main drawbacks of BCD are low selectivity towards aromatics, use of harsh reaction conditions, requirement of a neutralization step and reactor corrosion.31 To overcome this, some solid base catalysts such as porous metal-oxides hydrotalcites,32,33 Ni-supported layered double hydroxide hydrotalcite (Ni-HTC)34, and nitrate-intercalated hydrotalcite6 have been employed to depolymerize lignin.
Most reported studies employ model lignin compounds such as phenolic monomers and dimers. While these studies are useful in promoting a fundamental understanding of bond cleavage mechanisms with specific catalysts, they are not directly applicable to the deconstruction of real lignin.2 Several strategies for the deconstruction of polymeric lignin have been reported recently using hydrodeoxygenation35 and thermal catalytic depolymerization31.